One of the inherent problems associated with the use of contact lenses for vision correction is the tendency for inorganic and organic contaminants to accumulate on the lenses over time. As these deposits form, they may not only interfere with the wearer's vision, but can also cause discomfort and eventually may damage the lens.
While protease-containing compositions will quickly remove proteinaceous deposits from contact lenses, many inorganic deposits are not as easily removed. For example, removal of the common calcium chloride and calcium phosphate deposits generally requires that heat be applied to the lenses as part of a regular cleaning regime.
One approach to removing inorganic deposits from heavily soiled lenses is described in U.S. Pat. No. 4,395,346 to Kleist. In the disclosed method, the lenses are submersed in an aqueous solution containing a sequestering agent consisting of a polymetaphosphate, gluconic acid, and/or their salts. This solution is mechanically heated to between 40.degree. C. and 100.degree. C. (preferably at least 80.degree. C.), and is used to soak the lenses for extended periods (which can be shortened to 20 minutes or less where the lenses are also contacted with a protease).
While effective, this approach to removal of inorganic deposits has several drawbacks. Principal among these is the need to mechanically supply a sufficient level of heat to activate the sequestering agent and allow cleaning to occur in a reasonably short period of time. The need to use a mechanical heat source not only adds to the cost of contact lens use, it also requires the exercise of additional effort and skill to correctly clean the lenses. For example, if the lenses are exposed to too much heat they may be damaged.
A need, therefore, exists for a simple, self-activating system for limiting the accumulation of inorganic deposits on contact lenses. The present invention satisfies that need by providing compositions which assist in preventing deposits from accumulating on contact lenses without the use of externally supplied heat.